A motor of the above mentioned type is described in Swedish patent application No. 8700219-2. In this prior motor, the elongated body has magnetostrictive properties, whereby the motion required for advancing the driven member is brought about by axial displacement of the body.
The purpose of the present invention is to provide a motor of the type mentioned in the introduction, wherein the elongated body is stationary and the motion required for effecting the advance of the driven member is obtained by means of the elongation of the body.